BSOI wafers – Bonded SOI

Okmetic Bonded Silicon On Insulator wafers offer advanced platform for MEMS, sensor and power devices. In many cases BSOI wafers are more cost-effective choice than bulk silicon wafers. BSOI wafers have many benefits as they enable more ambitious device designs, improved device performance and smaller die size and they can be fully customized to meet your device and process needs.

Okmetic BSOI wafers are manufactured by bonding two silicon wafers together leaving an insulating buried oxide layer between them. Typically sensing elements and possible IC devices are built on the top wafer acting as a device layer. The buried oxide layer is an excellent electric insulating layer and it also forms an effective etch-stop in device manufacturing. It can also act as a sacrificial layer when manufacturing more complex devices such as released MEMS structures. The handle wafer is supporting the structure but can also be utilized in sealing the structure or as part of the sensing element. SOI wafers’ quality and cleanliness standards are identical with bulk silicon wafers.

Bonding enables thicker SOI device layer than competing technologies, which gives more device design freedom

Thanks to Okmetic’s bonding process, the device layer of the SOI wafer can be made much thicker than with competing SOI technologies, which gives more freedom to device design. The Bonded SOI wafer device layer can range from 1 μm to over 200 μm with standard thickness tolerance being ±0.5 µm and even ±0.1 µm with Enhanced SOI. Okmetic’s superior orientation accuracy capability can be utilized in both device layer and handle wafer, which enables smaller variation in customer’s device performance. Handle wafer thicknesses between 300 µm and 950 µm are possible and back surface can be polished or etched. Buried oxide is high quality thermally grown SiO2.

BSOI wafers are optimal for variety of devices

Okmetic BSOI wafer solutions are used e.g. for advanced pressure sensors, microfluidic components, MOEMS, flow sensors, actuators, 3-axis accelerometers, gyroscopes and silicon microphones. They also offer a new type of solution for the manufacture of high voltage devices such as gate drivers (IGBT/Power MOSFET), smart power/high voltage BCD and lateral HV devices. In addition, SOI wafers usage is expanding into RF field, for the needs of which Okmetic has developed High Resistivity SOI wafers. The possibility to tailor and modify parameters helps reach the full potential of any design idea in advanced device development.

Typical SOI specifications

Growth method Cz, MCz, A-MCz®
Diameter150mm, 200mm
Crystal orientation<100>, <110>,<111>
N type dopantsPhosphorus, red phosphorus
P type dopantsBoron
ResistivityFrom < 0.001 to > 7,000 Ohm-cm
Device layer thicknessFrom 1 μm to > 200 μm
Tolerance ±0.5 μm (standard BSOI), ±0.3 μm (0.3 SOI), ±0.1 μm (E-SOI®),  ±0.5 μm or lower (C-SOI®)
Buried oxide layer thicknessFrom 0.3 μm to 4 μm, typically between 0.5 μm and 2 μm
Type: thermal oxide
Handle wafer thicknessFrom 300 μm to 950 μm, typically 725 μm in 200mm wafer and 380 μm in 150mm
Back surfacePolished or etched

BSOI wafers enable more ambitious device designs cost-effectively

SOI wafers offer extremely cost-effective solution over bulk silicon micromachining. As an example, when manufacturing a pressure sensor on 400 µm thick wafer the cost per chip can be reduced by 33% with BSOI wafer compared to bulk silicon micromachining. This is because BSOI wafers allow smaller die sizes and more chips per wafer thus reducing the wafer, patterning, etching and bonding costs.

The BSOI wafer enables the design of more advanced applications thanks to its layered structure and possibility for a thicker device layer adding the design freedom. For example, expansion of smart power management integrations to include High Voltage driver circuits up to 100V or beyond are possible when using BSOI wafer as a platform.

BSOI wafer is an advanced solution with multiple benefits:

  • Reduced device size and cost
  • Improved device performance and precision
  • Increased device reliability
  • More advanced device designs

BSOI variations for specialized needs

0.3-SOI wafers

Okmetic 0.3-SOI is a bonded Silicon On Insulator wafer, which has buried oxide (BOX) layer between a bottom handle wafer and a top silicon wafer that is thinned with extra precision to achieve improved ±0.3 μm device layer thickness tolerance. This improved device uniformity is a relatively cost-effective solution enabling improved device performance and precision and additional freedom to device design. Even higher uniformity can be achieved with Okmetic E-SOI® wafers. The 0.3-SOI wafer is beneficial platform for many MEMS devices such as pressure sensors and resonators.

D-SOI wafers

Okmetic D-SOI is a bonded Silicon On Insulator wafer, that has two device and buried oxide layers with different thicknesses. The D-SOI wafer is beneficial platform for MEMS and photonics devices.

L-SOI wafers

Okmetic L-SOI is a bonded Silicon On Insulator wafer combining thick and highly doped device layer. This kind of Low Resistivity Bonded SOI wafer is beneficial in certain MEMS devices eg. silicon oscillators as no external packaging is needed unlike with quartz-based oscillators. This leads to reduced board size an absence of quality issues with external chips.

Thick SOI wafers

Okmetic Thick SOI is a bonded Silicon On Insulator wafer with very thick device layer. The bonding process enables the manufacture of very thick, over 200 μm SOI device layers that would not be possible with other competing technologies.

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